addHeaderField

The header name must begin with "Content-" or this method does
nothing. The header field can span several multiple lines as long as line
endings are marked with a carriage-return line-feed pair (CRLF).

Examples

"Content-Internal: Message for Internal Use Only"
"Content-Internal: Message for Internal Use Only; value=internal"

Parameters:

headerField - Header field for this part, including header name and value.